Extra Sidekiq processes

GitLab Enterprise Edition allows one to start an extra set of Sidekiq processes besides the default one. These processes can be used to consume a dedicated set of queues. This can be used to ensure certain queues always have dedicated workers, no matter the number of jobs that need to be processed.

Starting extra processes via Omnibus GitLab

To enable sidekiq-cluster, you must apply the sidekiq_cluster['enable'] = true setting /etc/gitlab/gitlab.rb:

sidekiq_cluster['enable'] = true

You will then specify how many additional processes to create via sidekiq-cluster as well as which queues for them to handle. This is done via the sidekiq_cluster['queue_groups'] setting. This is an array whose items contain which queues to process. Each item in the array will equate to one additional sidekiq process.

As an example, to make additional sidekiq processes that process the elastic_indexer and mailers queues, you would apply the following:

sidekiq_cluster['queue_groups'] = [
  "elastic_indexer",
  "mailers"
]

To have an additional sidekiq process handle multiple queues, you simply put a comma after the first queue name and then put the next queue name:

sidekiq_cluster['queue_groups'] = [
  "elastic_indexer,elastic_commit_indexer",
  "mailers"
]

Keep in mind, all changes must be followed by reconfiguring your GitLab application via sudo gitlab-ctl reconfigure.

Monitoring

Once the Sidekiq processes are added, you can visit the “Background Jobs” section under the admin area in GitLab (/admin/background_jobs).

Extra sidekiq processes

All queues with exceptions

To have the additional sidekiq processes work on every queue EXCEPT the ones you list:

  1. Edit /etc/gitlab/gitlab.rb and add:

    sidekiq_cluster['negate'] = true
    
  2. Save the file and reconfigure GitLab for the changes to take effect.

Limiting concurrency

  1. Edit /etc/gitlab/gitlab.rb and add:

    sidekiq_cluster['concurrency'] = 25
    
  2. Save the file and reconfigure GitLab for the changes to take effect.

Keep in mind, this normally would not exceed the number of CPU cores available.

Modifying the check interval

To modify the check interval for the additional Sidekiq processes:

  1. Edit /etc/gitlab/gitlab.rb and add:

    sidekiq_cluster['interval'] = 5
    
  2. Save the file and reconfigure GitLab for the changes to take effect.

This tells the additional processes how often to check for enqueued jobs.

Starting extra processes via command line

Starting extra Sidekiq processes can be done using the command /opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster. This command takes arguments using the following syntax:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster [QUEUE,QUEUE,...] [QUEUE, ...]

Each separate argument denotes a group of queues that have to be processed by a Sidekiq process. Multiple queues can be processed by the same process by separating them with a comma instead of a space.

Instead of a queue, a queue namespace can also be provided, to have the process automatically listen on all queues in that namespace without needing to explicitly list all the queue names. For more information about queue namespaces, see the relevant section in the Sidekiq style guide.

For example, say you want to start 2 extra processes: one to process the “process_commit” queue, and one to process the “post_receive” queue. This can be done as follows:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit post_receive

If you instead want to start one process processing both queues you’d use the following syntax:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit,post_receive

If you want to have one Sidekiq process process the “process_commit” and “post_receive” queues, and one process to process the “gitlab_shell” queue, you’d use the following:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit,post_receive gitlab_shell

Monitoring

The sidekiq-cluster command will not terminate once it has started the desired amount of Sidekiq processes. Instead, the process will continue running and forward any signals to the child processes. This makes it easy to stop all Sidekiq processes as you simply send a signal to the sidekiq-cluster process, instead of having to send it to the individual processes.

If the sidekiq-cluster process crashes or receives a SIGKILL, the child processes will terminate themselves after a few seconds. This ensures you don’t end up with zombie Sidekiq processes.

All of this makes monitoring the processes fairly easy. Simply hook up sidekiq-cluster to your supervisor of choice (e.g. runit) and you’re good to go.

If a child process died the sidekiq-cluster command will signal all remaining process to terminate, then terminate itself. This removes the need for sidekiq-cluster to re-implement complex process monitoring/restarting code. Instead you should make sure your supervisor restarts the sidekiq-cluster process whenever necessary.

PID files

The sidekiq-cluster command can store its PID in a file. By default no PID file is written, but this can be changed by passing the --pidfile option to sidekiq-cluster. For example:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster --pidfile /var/run/gitlab/sidekiq_cluster.pid process_commit

Keep in mind that the PID file will contain the PID of the sidekiq-cluster command and not the PID(s) of the started Sidekiq processes.

Environment

The Rails environment can be set by passing the --environment flag to the sidekiq-cluster command, or by setting RAILS_ENV to a non-empty value. The default value is “development”.

All queues with exceptions

You’re able to run all queues in sidekiq_queues.yml file on a single or multiple processes with exceptions using the --negate flag.

For example, say you want to run a single process for all queues, except “process_commit” and “post_receive”. You can do so by executing:

sidekiq-cluster process_commit,post_receive --negate

For multiple processes of all queues (except “process_commit” and “post_receive”):

sidekiq-cluster process_commit,post_receive process_commit,post_receive --negate

Limiting concurrency

By default, sidekiq-cluster will spin up extra Sidekiq processes that use one thread per queue up to a maximum of 50. If you wish to change the cap, use the -m N option. For example, this would cap the maximum number of threads to 1:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit,post_receive -m 1

For each queue group, the concurrency factor will be set to min(number of queues, N). Setting the value to 0 will disable the limit.

Note that each thread requires a Redis connection, so adding threads may increase Redis latency and potentially cause client timeouts. See the Sidekiq documentation about Redis for more details.

Number of threads

Each process started using sidekiq-cluster (whether it be via command line or via the gitlab.rb file) starts with a number of threads that equals the number of queues, plus one spare thread. For example, a process that handles the “process_commit” and “post_receive” queues will use 3 threads in total.